Field of the Invention
The present invention relates to a method of etching a silicon substrate.
Description of the Related Art
U.S. Pat. No. 5,501,893 and Japanese Patent Application Laid-Open No. 2006-148156 disclose techniques of forming a trench in a silicon substrate (hereinafter, also “Si substrate”) by a dry plasma etching. In the methods of U.S. Pat. No. 5,501,893 and Japanese Patent Application Laid-Open No. 2006-148156, for an Si substrate on which an etching mask has been formed, the deposition of a protection film, the etching of the protection film and the etching of the Si substrate are repeated so that a trench is formed in the Si substrate.
In the deposition step, the protection film is formed on the surface of the etching mask, the sidewall of the trench, and the bottom of the trench. In the etching step for the protection film, a bias is applied to substrate electrodes, directionality is given to ions in the plasma, and the protection film formed on the bottom of the trench is removed. On this occasion, the protection film formed on the sidewall of the trench remains without being removed. Next, in the etching step for the Si substrate, a portion of the Si substrate exposed from the protection film at the bottom of the trench is etched. Thereafter, these deposition step and etching steps are repeated so that the trench is formed in the Si substrate.